The main purpose of this research is to create suitable animal models for phenylketonuria for the purpose of elucidating cerebral biochemical abnormalities in developing brain which lead to mental retardation. In focusing attention on enzymes in glycine metabolism and on the formation of catecholamines, we also hope to detect chemical abnormalities in the brain which may be the common consequence of several aminoacidopathies and thus the common basis for the ensuing deficit in cerebral functions.